The trajectory of ink-jet droplets: Modelling and experiment

A simple experimental arrangement was used to study the trajectories of droplets ejected by an ink-jet printer. Droplets with an average diameter of 224μm were ejected from a nozzle with an orifice of 76μm. The recorded flight path was used to find the drag force, deceleration and hence the loss of height when the droplets were ejected horizontally. Using various approaches for semi-turbulent flow, good fits for trajectory were obtained. A model was developed to include the effect of the change in droplet shape from cylinder to sphere during flight but this did not improve trajectory fit. Methods for calculation of exit velocity produced deviations of 4–15% from the value measured by high-speed photography.